Accept an input source-map, for generating the final source-map

[binyamin]

When a stylesheet has a source-map from a previous transformation, use it to generate the new source-map.

Use-case: A user might transform .scss files into CSS, and then minify it with parcel-css.

[devongovett]

Parcel already does this. I assume you mean when using the Parcel CSS CLI?

[binyamin]

@devongovett Nope. I'm using @parcel/css-wasm, in Deno. Either way, I looked through the Readme and the type definitions. I couldn't find any options which accepted a source-map.

[devongovett]

We could support data urls in a sourceMappingURL comment, but referencing files on the filesystem or external URLs won't be supported because Parcel CSS doesn't do any filesystem operations (in WASM there is no access anyway).

I suppose we could also support a separate input string for the source map, but handling that is already possible using Parcel's source map library. Something like this:

const {transform} = require('@parcel/css');
const SourceMap = require('@parcel/source-map');

let result = transform({ /* ... */ });

let prevMap = new SourceMap(PROJECT_ROOT_DIR);
prevMap.addVLQMap(previousSourceMapJSON)

let map = new SourceMap(PROJECT_ROOT_DIR);
map.addVLQMap(JSON.parse(result.map.toString()));
map.extends(prevMap);

[binyamin]

@devongovett Thank you. By the way, what does the PROJECT_ROOT_DIR variable do here? Just wondering.

[devongovett]

All file paths in the source map are stored relative to the project root directory. Typically it'll be the root of your git repository, for example.

Btw, I'm working on support for data urls in sourceMappingURL comments. Will open a PR here once parcel-bundler/source-map#109 is merged.